Travelling wave tube



July 12, 1960 R, BlTTMAN EI'AL 2,945,154

TRAVELLING WAVE TUBE Filed Jan. 18, 1957 INVENTORS LORAN R. BITTMAN NORMAN M. GUTLOVE RIHARD D. GEYER ATTORNEY United Stts TRAVELLING WAVE TUBE Loran R. Bittman, Fresh Meadows, Norman M.. Gutlove,

lronx, and Richard D. Geyer, Manhasset, NSY., asslgnors to SperryARand Corporation, a corporation of Delaware Filed Jan. 18, 1957, Ser. No. 635,042

2 Claims. (Cl. 315-35) The present invention relates to microwave coupling and magnetic beam controlling means for travelling wave tube devices.

It is'requi'red in travelling wave tubes tc produce and direct Aan electron beam whose diameter remains constant along a slow wave propagating structure such as ahelix. This is generally accomplished in high powered tubes by providing a beam which is initially elec- 'trostatically focussed and converges from the gun cathode vto a, minimum diameter at a predetermined point withinf an aperture through a magnetic pole piece between the electron gun and helix, the beam being controlled along, the helix by an axial magnetic field established between the aforementioned pole piece and a fur- 'ther pole piece atv the output end of the tube.

As is disclosed in U.S. Patent 2,707,758 in the name of C. Wang', dated May 3, 1955, if the beam electrons from' 'the' gun, are' made to enter without radial velocity into a magnetic field of proper flux Idensity curving into thepole piece at the input end of the tube, a magnetic iield of minimum flux density may be utilized between sucha pole piece and the further pole piece at the output end of the tube forV causing the beam electrons to travel inhelic'al paths of constant radii within the slow wave propagating helix. A problem arises in such a device, however, inV coupling the helixY to input and output microwave transmission devices without disturbing the uniformity of the axial magnetic iield along the helix required for satisfactory control of the beam. It has been found that interruptions in the magnetic field can Ycause severe defocussing problems and degrade the tubes performance dueto beam interception by the helix in theh vicinity ofV such interruptions.

Therefore, it is an object of the present invention to provide an: improved travelling wave tube device having magnetic beam controlling means together with electromagnetic coupling means for supplying and deriving microwave energy from the slow wave propagating structureofthe tube without causing any significant disturbance in the uniformity of an axial magnetic beam-controlling Held.

t lis `another object of the invention to provide a travelling wave tube having input and output transmission, line coupling devices connected to the slow wave propagating structure of the tube, the coupling devices being supported by magnetic pole piece assemblies at the Ainput. and output of the tube.

-It is: a further object of the present invention to provide a device. as aforedescribed which is of rugged and compact construction.

The foregoing together with other objects and advantages of the present invention, which will become more apparent from the detailed description thereof, are attained by ,providing tirst'and second magnetic pole piece means positioned at opposite ends of -the slow wave propagating structure of a travelling wave tube for providing: terminating paths for an axial magnetic field vof the pole pieces.

2,915,154` Patented July 12, 1960 established between the pole pieces by means such as a solenoid extending between the pole pieces, the ends of the solenoid being closely adjacent respective ones Each end of the slow Wave propagating structure is terminated in the vicinity of an axial aperture through a respective lone of the pole piece means, the pole piece means including transverse aperture means for receiving input and an output microwave coupling devices', respectively, for exchange of energy with the slow wave propagating structure. Thus, a uniform axial magnetic iield can be established between the pole piece means from one end of the slow wave propagating structure to the other for optimum control of the electron beam therealong, the coupling devices providing substantially no interruption in the axial magnetic eld controlling the beam.

Referring to the drawings,

Fig. l is a View, partly in section, of a travelling wave tube device having a magnetic focussing assembly and external transmission line coupling devices associated therewith in accordance with the present invention;

Fig. 2 is a cross-sectional view of the device taken along the line 2 2 in Fig. 1; and,

Fig. 3 is a further cross-sectional view of the device taken along the line 3-3 in Fig. l.

Referring now to Fig. l, the travelling wave tube of the present invention includes an electron gun assembly 11 for producing and directing an electron bea-m through a conductive helix 12 in alignment therewith, the beam being received at theoutput end of the helix 12 by a collector assembly 13 also axially aligned with the helix. 'Ille `inner conductors of input and output coaxial line connector'assembliesl and 174 are connected, to the opposite ends of the helix `12, respectively, for coupling the helix l2 to input and output external microwave devices, respectively.

The electron gun assembly 11 includes a spherically concave cathode. button 19, a focussing ring electrode 2n and an apertured accelerator electrode 21 positioned in coaxial alignment as shown in Fig. l forp'roviding an electron beam. The electron beam is initially con- Vvergen't and focussed electrostatically by the electrodes 2d and 2i. to convergeY to a minimum diameter at a predetermined region `within the, aperture of electrode 2l prior to entry of the beam into the heini The design of the electron gun l1 is generally similarto 'that described in the aforementioned U.S. Patent 2,707,758.

The electrode 21 is comprised of a cylindrical block of highly permeable Imagnetic material having appreciable thickness along -the axis of thetube. Blockl'Z includes an axial. aperture 22 for passage of the electron beam therethrough. Block 21 also includes a radial aperture extending in a direction transverse the axis of helix 12 from aperture 22 to the exterior' of block 2l for receiving the-coaxial line receptacle 16 as Ash'ovvn in Fig. l. Receptacle 16 is brazed to the wall of the aforementioned radial aperture in` block 21 for preserving a vacuum seal for the tube, suitable means also being provided within receptacle 17 between the inner and outer conductors thereof forV preserving the aforementioned vacuum.

The collector electrode 13 is conventional in-the art, being similar tothat shown and described in copending U.S. application Serial No. 520,445, led on July 7, 1955, in the name of John ldDe4 Prado, for example, now U.S. Patent No. 2,863,078, issued November 2, 1,958. A planar surface 23 and an inner cylindrical surface 24 of the assembly 13 receives the beam electrons after they have passed through the helix 12. 1

The collector electrode assembly 13 is brazed' 1ro-a cylindrical block 28 of highly permeable magnetic material positioned on the helix side of assembly 13. The block 28 has a coaxial aperture 29 therethrough for passage of the beam at the output end of the tube into the collector electrode assembly 13, the aperture 29 being flared at its right hand end for insuring that none of the beam electrons are intercepted thereby. The block 28 also includes a radial aperture therein extending in a direction transverse the axis of helix 12 from aperture 29 to the exterior of block 28 for insertion of the output coaxial line assembly 17 Whose inner conductor is connected to the end of helix 12 as shown. The outer conductor of connector 17 is permanently xed, as by brazing, to `the wall of the aforementioned radial aperture in block 28 so as to preserve `a vacuum seal. Suitable means are provided between the inner and outer conductors of receptacle 17 for further preservation of the vacuum.

The helix 12 is supported in coaxial alignment with the electron gun and collector assembly 11 and 13, respectively, by means of three dielectric rods designated by numerals r31 supported by and extending from the block 21 to the block 28. The three rods 31 are spaced apart around the axis of the tube so as to be 120 apart, the ends of each of rods 31 being received in suitable grooves provided `along the inner coaxially apertured wall of each of blocks 21 and 28, respectively.

The space along the helix 12 is sealed off in a vacuum by means of input and output metallic transition sections 33 and 34 and an intermediate metallic cylindrical section 35 connected therebetween as by brazing. The members 33 and 34 are brazed to the blocks 21 and 28 to thereby form a rugged tubular construction. The cylindrical section 35 should be of sucient radius such as the order of three times the radius of the helix 12 so as to have only a very small effect on the axial component of the electric elds of the helix for microwave energy propagated therealong.

The transition sections 33 and 34 together with the portions of blocks 21 and 28 between such sections and the input and output connector sections, respectively, effectively comprise continuations for microwave energy of the outer conductors of the coaxial line connectors 16 and 17, respectively. The coaxially apertured inner surfaces of sections 33 and 34 are iiaredY as shownV for providing impedance matched transitions between coaxial line and helix energy at the input and output ends of the tube. The particular design of the aforementioned Y2,945,154Y Y e e' transition sections is determined in accordance with the 37 in coaxial alignment with the radial aperture in blockI 21 so that room is provided for insenting the coaxial line connector assembly 16 into the block 21.

The block 28 forming part of the pole piece means at the output end of the tube includa a radial flange section 39 of highly permeable magnetic material having a radial groove 40 in coaxial alignment with the radial aperture in block 28 for receiving the coaxial line connector device 17 as illustrated in Fig. l. The output pole piece assembly means is further comprised ofv apertured plate like member 41 of highly permeable magnetic material adjacent the flanged extension 39 of block 28 in face to face abutment thereagainst. The aperture through member 41 is substantially coaxial with the tube axis, the aperture having a suiciently large radius so that member 41 does not cause the magnetic field along helix 12 to diverge prematurely before entering the main body 28 of the output pole piece means.

Three L-shaped members 42 axed by screws 43 to the flange 39 are provided around flange 39 at intervals of A leg of each of members 42 contains a threaded aperture and a screw 44 extending therethrough radially of the axis of the tube with the ends of the screws 44 supporting the apertured Vplate member 41. The screws 44 are adjustable for regulating the axial relationship between the plate like member 41 and the axis of helix 12. 1

A tubular form 46 of non-ferromagnetic material is supported between the two plate members 36 and 41, each plate member being provided with a circular groove therein for receiving form 46. The form 46 is provided for the purpose of supporting a sectionalized solenoid comprised of winding sections 47, 48 and 49 along the tube as is shown in Fig. 1. Each of the winding sections is provided with a separate source of potential not shown, for energizaton thereof, thin non-ferromagnetic spacer elements 51-54 separating the winding sections from each other and the solenoid from the pole piece members 36 and 41. Since one end of the solenoid supporting form 46 is mounted upon the plate member 41 whose radial position can be regulated by screws 44, the axial position of the solenoid structure can be changed slightly relative to the axis of the electron beam for obtaining optimum magnetic control of the beam at output end of the helix 12. Further control of the magnetic eld at the input and output ends of the tube is attained by utilizing the separately energized winding sections 47 and.49, the lux provided by each winding section depending on the degree of energizaton thereof.

The operation of the tube is conventional to travelling Wave tubes known in Ithe art. Each of the solenoid sections 47-49 is suitably energized for establishing a magnetic field which is axial along helix 12 and curves into the input and output pole piece means within apertures 22 and 29 of blocks 21 and 28, respectively, the field strength along the axis of helix 12 being substantially uniform. The electron beam, which s initially focussed electrostatically by the gun 11, converges to a minimum diameter slightly less than that of helix 12 at a predetermined point within the aperture 22 of pole piece 21 prior to entry into the helix 12. The face of pole piece 21 opposite cathode 19 comprises an accelerator electrode plane for the gun. The minimum diameter of the beam is made by proper design of the gun 11, in accordance with the principles disclosed inthe aforementioned U.S. Patent 2,707,758, to occur at the eective plane of entrance into the magnetic eld established within the aperture 22 of the input pole piece means by the solenoid sections 47-49. The beam electrons are thereafter caused by the magnetic flux to travel in helical paths of constant radii along the axis of helix 12 with the boundary of the beam being contained within the helix in close relationship with the turns thereof by the axial component of magnetic flux extending through helix 12.

The sectionalized solenoid means 47-49 extend axially of the tube substantially from one to the other of the pole piece members 36 and 41 so there is no undesired air gap between the solenoid and input and output pole piece means which might cause an interruption in uniformity in the axial magnetic field between the pole piece assemblies. The coaxial line connector assemblies 16 and 17 are close enough to the solenoid means so that the axial portion of the magnetic field will extend all the way through helix 12 before diverging into the pole piece assemblies, the ends of the helix 12 extending only a short distance `into the axial apertures 22 and 29 of the pole piece members 21 and 28, respectively. The magnetically permeable plate member 36 of the input pole piece meansv between the coaxial line connector assembly 16 and the solenoid should only be thick enough to be structurally rigid and provide a continuous and symmetrical ferromagnetic path between the left hand end of the solenoid and the main body 21 of the input pole piece means without becoming magnetically saturated. This is desired since further insurance of the uniformity of the axial component of magnetic eld along the helix 12 at its left hand end is provided.

The magnetically permeable plate like member 41 of the output pole piece means together with the portion of flange 3-9 between the output connector assembly 17 should also be thick enough to be structurally rigid and provide a continuous and symmetrical ferromagnetic pa-th between the right hand end of the solenoid and the main body 28 of the output pole piece means without becoming magnetically saturated. In general, the output pole piece means should be designed and the coaxial line connector assembly located therein so that the axial component of the magnetic eld at the output end of helix 12 is substantially uniform for insuring that the beam does not diverge prematurely before passing through the helix. If the beam were to diverge too soon, the beam electrons would be intercepted by the end turns of the helix 12 and/0r the connection from helix 12 to the inner conductor of assembly 17 and cause the aforementioned turns or connection to burn out. The Vaforementioned connection from helix 12 to the inner conductor of assembly 17 should be as close to the left hand face of the magnetically permeable member 28 as feasible since the. axial component of the magnetic flux becomes decreasingly less proceeding to the right along Iaperture 29 of the member 28.

It has been found that the provision of the radial apertures in the input and output pole piece assemblies for receiving the coaxial line receptacle devices 16 and 17 do not unduly disturb the symmetrical uniform eld distribution of the axial magnetic field through the helix in the region of the beam. Therefore, control of the beam is not affected by the aforedescribed radial apertures nor the coaxial line receptacle devices therein, so that a highly practical and eicient tube assembly is provided by the present invention.

While the invention has been described in its preferred embodiments, it is to be understood that the words which have been used are words of description rather than of limitation and that changes within the purview of the appended claims may be made Without departing from the true scope and spirit of the invention in its broader aspects.

What is claimed is:

1. An electron beam tube comprising a vacuum envelope that contains means for producing and directing an electron stream along a predetermined path within said envelope, a magnetic pole piece forming part of said envelope, said pole piece having a iirst aperture in said path for passage of the stream through the pole piece, means including said pole'piece for producing a magnetic field that maintains the diameter of said stream substansaid ii-rst aperture to the exterior of the pole piece -in a transverse direction, a section of transmission line supported in `said second aperture in vacuum sealed relationship with the wall of said second aperture, a slow wave propagating structure for carrying electromagnetic energy which interacts with said stream, and means for coupling one end of said slow `wave propagating structure to one end of said section of transmission line.

2. A travelling Wave tube comprising a vacuum envelope that contains means including a cathode and an anode'for producing an electron stream within said envelope, a collector electrode for receiving said stream, first and second magnetic pole pieces located at the anode end and the collector end of said tube, respectively, each of said pole pieces Iforming part of said vacuum envelope and having a rst aperture for passage of said stream therethrough, a solenoid magnet extending from one to the other of said pole pieces for producing a magnetic field that maintains the diameter of said stream substantially constant between said pole pieces, a slow Wave helix disposed within said magnet for passage of the stream therethrough, the ends of said helix -being terminated with the first apertures of said pole pieces, respectively, each of said pole pieces having a second aperture that extends from said rst aperture to the exterior of the pole piece in a transverse direction, and a pair of coaxial line sections supported Within the second apertures of said pole pieces in vacuum sealed relationship with .the walls of said second apertures, respectively, the inner conductors of said coaxial lines extending into the iirst apertures of said pole pieces for connection to the respective ends of said helix.

References Cited in the ile of this patent UNITED STATES PATENTS 2,727,179 Lally et al. Dec. 13, 1955 2,788,465 Bryant et al. Apr. 9, 1957 2,798,203 Robertson July 2, 1957v 2,812,467 Kompfner Nov. 5, 1957 2,812,470 Cook et al. Nov. 5, 1957 2,829,299 Beck Apr. 1, 1958 2,843,790 (hitler July 15, 1958 FOREIGN PATENTS 153,259 Australia Sept. 17, 1953 OTHER REFERENCES RCA Magnetrons and Traveling-Wave Tubes, by Radio Corporation of America, Tube Division, Harrison, New Jersey, June 1956, 39 pages; only pages 19 and 20 relied on. 

